Behavior

Male Thick-billed Vireos generally sing or chatter in response to hearing an intruder in his territory, though some approach silently. Females sometimes chatter in response to intruders, and sometimes approach as well. Males are very aggressive towards conspecific intruders as well as White-eyed Vireo (Vireo griseus) intruders; most attacked taxidermy mounts, and some ripped out feathers and removed eyeballs from the mounts. During agonistic interactions, the male often puffs out his chest feathers, attains an exaggerated upright posture, and spreads his tail feathers, especially if his mate is present.  When agitated and searching for an intruder, they flick their wings.

Thick-billed Vireos are very bold, and will often approach people within a couple of meters. One individual, after being caught, banded, and measured, perched on the author's finger, staying even while being filmed.

Thick-billed Vireo pairs maintain territories year-round. Males are involved in territory defense. Females may approach and vocalize (chatter call) but do not attack intruders. Average territory size is 1.5 ha (unpublished data). Males regularly sing throughout the year, and both sexes vocalize towards neighbors at territory boundaries.

Socially monogamous. The extent of extrapair copulations is unknown.

Solitary floaters or territorial pairs year-round; does not join mixed species flocks or aggregations. Individuals without territories are solitary.

Thick-billed Vireo remains were found in Barn Owl (Tyto alba) pellets in The Bahamas (Olson et al 1990). An individual in Florida was captured by a raptor (Smith et al 1990). One individual was caught by an American Kestrel (Falco sparverius) on Cayo Paredon Grande (Kirkconnell and Garrido 1991).